The special case of \(n=4\)  and \(k=6\) , being the most common commercial version of Mastermind, has received some special attention. Knuth [1]} showed that the optimal deterministic strategy needs 5 guesses in worst case. In the randomized setting, it was shown by Koyama [2]} that optimal strategy needs in expectation \(5625/1296 = 4.34\dots \)  guesses for the worst case distribution of codewords.
